06-18-2008, 10:51 PM
Hi Guys,
I had recapped a set not long ago, a Philco 38-3, and when it came to the plate caps I was advised that the 630v caps might work fine.
On the other hand someone else said that there may be a spike or transient voltage could occasionally occur, such as from changing the bandswitch or a loud crash of static that would raise that voltage over the 630v rating.
"Fast transients in the output stage can induce very high voltages on the plates of the output tubes. Those caps can be thought as snubbers to provide some protection from over voltage and they meant it when they used high voltage caps. Observing the startup voltage transient won't give you the story on them. Driving the audio stage into clipping will show just how high they can go. "
There was also talk about if Philco thought they needed a 1000v cap in there it must have been a good reason.
There was a pretty good discussion about this issue on 'the other' forum, you might find interesting:
http://antiqueradios.com/forums/viewtopi...&highlight=
I did replace the two plate caps with the 1000v rating since I had the set out.
So, maybe I didn't need them, or possibly those points were valid, I don't know. I didn't want to take a chance with something with a lower rating.
I just thought I'd throw that out to you all and see what you think.
Take care,
Gary.
I had recapped a set not long ago, a Philco 38-3, and when it came to the plate caps I was advised that the 630v caps might work fine.
On the other hand someone else said that there may be a spike or transient voltage could occasionally occur, such as from changing the bandswitch or a loud crash of static that would raise that voltage over the 630v rating.
"Fast transients in the output stage can induce very high voltages on the plates of the output tubes. Those caps can be thought as snubbers to provide some protection from over voltage and they meant it when they used high voltage caps. Observing the startup voltage transient won't give you the story on them. Driving the audio stage into clipping will show just how high they can go. "
There was also talk about if Philco thought they needed a 1000v cap in there it must have been a good reason.
There was a pretty good discussion about this issue on 'the other' forum, you might find interesting:
http://antiqueradios.com/forums/viewtopi...&highlight=
I did replace the two plate caps with the 1000v rating since I had the set out.
So, maybe I didn't need them, or possibly those points were valid, I don't know. I didn't want to take a chance with something with a lower rating.
I just thought I'd throw that out to you all and see what you think.
Take care,
Gary.
